Traditionally, processors (such as the Pentium series from Intel, Athlon series from AMD, etc) have become faster by supporting ever-increasing clock speeds. As processors got faster in this way, the time used up to run a particular piece of software on these processors automatically sped up proportionally (because the time to execute a single instruction of code is roughly proportional to the speed of the processor clock).
New generations of processors being released today, however, are not using clocks that are significantly faster than they were two years ago (about 3 GHz). Instead, these processor chips now include more than one processor inside them (e.g., Pentium D processors are “dual core,” meaning they have two mini-processors in one chip). This property enables the computer to simultaneously run several “threads” of execution, or run software in parallel.